1. Field of the Invention
The present invention relates to an injection molding machine, and especially relates to an injection molding machine provided with a pressure monitoring device for the inside of the injection molding machine.
2. Description of the Related Art
In an injection device of an injection molding machine, resin which is melted at a high temperature is poured into a mold which is fixed to a platen so as to form a molded article. In an injection operation, highly-heated resin is injected at high speed and high pressure. The resin is extremely highly heated, so that the periphery of a nozzle from which the resin is jetted is mainly covered by a safety cover or the like for safety of an operator so as to secure safety.
A maintenance work is sometimes performed while opening a safety cover. At this time, safety is secured by disabling the injection molding machine. In addition to this disabling, it is necessary to pay sufficient attention to a highly-heated nozzle and a highly-heated member such as melted resin in the injection molding machine. Especially, when melted resin in the nozzle tip is cooled and solidified to clog a hole on the nozzle tip, the melted resin inside the nozzle is maintained in a high pressure state even in a state in which the injection molding machine is stopped. Then, when the solidified resin in the nozzle tip is melted again and the clogging is eliminated, the resin may jet out from the nozzle. Therefore, it is necessary to perform the maintenance work while constantly paying attention to the state of the nozzle and the state of the pressure inside a cylinder.
Further, in a state in which a nozzle is brought into contact with a mold, that is, in a nozzle touch state, melted resin may jet toward a mold clamping device from the nozzle through the mold.
In Japanese Patent Application Laid-Open No. 51-67577, a door switch for a door serving as a safety cover, a rotation detection mechanism which detects presence/absence of rotation of a motor inside an injection molding machine, and a door locking mechanism are provided as safety measures by a safety cover of the injection molding machine. When the door is opened, a power source is turned off so as not for the motor to rotationally drive. When the motor rotates, the door is locked by the door locking mechanism.
Japanese Patent Application Laid-Open No. 2013-188875 discloses a technique in which when opening of a safe door is detected by a safe door position detection switch, a nozzle is retracted so as not to generate a nozzle touch force and thus, safety of an operator is secured in a nozzle touch force control device of an injection molding machine.
Japanese Patent Application Laid-Open No. 2003-80358 discloses a technique in which a shield plate is inserted between a fixed mold and a movable mold in synchronization with an opening movement of a safe door of an injection molding machine so as to secure safety in taking out a metal molded article.
Japanese Patent Application Laid-Open No. 2014-28491 discloses a technique in which pressure is monitored and a screw is retracted when a safety cover is opened at time or after stop of a forward movement instruction of an injection device and before start of a retracting instruction in a state in which a nozzle is abutted on a nozzle touch unit in an injection molding machine.
In the techniques disclosed in Japanese Patent Application Laid-Open No. 51-67577, Japanese Patent Application Laid-Open No. 2013-188875, and Japanese Patent Application Laid-Open No. 2003-80358, rotation of the motor of the machine is stopped and resin inside is prevented from jetting out when the safety cover is opened. However, the pressure inside the nozzle is maintained at high pressure, so that when the clogging of the nozzle is eliminated, resin may jet out to expose an operator to dangers.
In the technique disclosed in Japanese Patent Application Laid-Open No. 51-67577, the locking mechanism for the safety cover is released in response to the stop of the rotation of the motor in the machine. Here, when the pressure inside the cylinder is high, resin may jet out when the safety cover is opened.
In the technique disclosed in Japanese Patent Application Laid-Open No. 2013-188875, the nozzle touch force is released when the safety cover is opened, but resin may jet out when the nozzle touch state is not generated.
In the technique disclosed in Japanese Patent Application Laid-Open No. 2003-80358, a safety cover covering a gate portion of the mold is merely provided, so that resin may jet out when a maintenance work around the gate portion is performed.
In the technique disclosed in Japanese Patent Application Laid-Open No. 2014-28491, a shaft needs to be operated in the safety cover opened state at which the operation should be stopped as a main body emergency stop state, so that an operator may be exposed to dangers. Further, the pressure is monitored only in the nozzle touch state, so that resin may jet out when the clogging of the nozzle is eliminated.
It is difficult to recognize a state in which a nozzle is clogged and a state in which the pressure inside a cylinder is high even by visually inspecting the nozzle and the cylinder, so that an operator may perform the maintenance work without recognizing a dangerous state in which resin jets out.